Climatic Change

, Volume 111, Issue 2, pp 487–495 | Cite as

Increasing prevalence of extreme summer temperatures in the U.S.

A Letter
  • P. B. DuffyEmail author
  • C. Tebaldi


Human-caused climate change can affect weather and climate extremes, as well as mean climate properties. Analysis of observations and climate model results shows that previously rare (5th percentile) summertime average temperatures are presently occurring with greatly increased frequency in some regions of the 48 contiguous United States. Broad agreement between observations and a mean of results based upon 16 global climate models suggests that this result is more consistent with the consequences of increasing greenhouse gas concentrations than with the effects of natural climate variability. This conclusion is further supported by a statistical analysis based on resampling of observations and model output. The same climate models project that the prevalence of previously extreme summer temperatures will continue to increase, occurring in well over 50% of summers by mid-century.


Bias Correction Global Climate Model Natural Climate Variability Extreme Summer Temperature Gridded Observational Dataset 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



Claudia Tebaldi acknowledges support from the US Department of Energy, Office of Biological and Environmental Research, grant DE-SC0004956 and thanks the Climate and Global Dynamics division of the National Center for Atmospheric Research, Climate Change Research section, for hosting her.

Supplementary material

10584_2012_396_MOESM1_ESM.pdf (816 kb)
Figure S1 Like Fig. 1 but here we set to 5% all values that are not determined significantly different from 5% on the basis of the bootstrap procedure described in detail in the Materials and methods section. (PDF 816 kb)
10584_2012_396_MOESM2_ESM.pdf (268 kb)
Figure S2 Ratio of the value of a linear trend fitted to the 50 year period 1950–1999 (in degrees Celsius per year) divided by the inter-annual standard deviation computed on the same 50 year period, for the two observational datasets top row and the ensemble of GCM simulations (presented here as the ensemble average ratio). These results confirm the different magnitude of this ratio in the different regions that the analysis of exceedance has highlighted. Note that observations in some regions show negative trends, while the ensemble average of the GCMs do not, consistent with the idea that negative trends are caused by internal variability that is not replicated consistently and simultaneously across the ensemble of models. (PDF 267 kb)


  1. Anderson BT (2011a) Intensification of seasonal extremes given a 2°C global warming target. Clim Chang. doi: 10.1007/s10584-011-0213-7, online first
  2. Anderson BT (2011b) Near term increase in frequency of seasonal temperature extremes prior to the 2°C global warming target. Clim Chang 108(3):581–589CrossRefGoogle Scholar
  3. Battisti DS, Naylor RL (2009) Historical warnings of future food insecurity with unprecedented seasonal heat. Science 323(5911):240–244CrossRefGoogle Scholar
  4. Christidis N, Stott PA, Zwiers FW, Shiogama H, Nozawa T (2010) Probabilistic estimates of recent changes in temperature forced by human activity: a multi-scale attribution analysis. Clim Dynam 34:11391156. doi: 10.1007/s00382-009-0615-7 CrossRefGoogle Scholar
  5. Diffenbaugh NS, Ashfaq M (2010) Intensification of hot extremes in the United States. Geophys Res Lett 37:L15701. doi: 10.1029/2010GL043888 CrossRefGoogle Scholar
  6. Diffenbaugh NS, Scherer M (2011) Observational and model evidence of global emergence of permanent, unprecedented heat in the 20th and 21st centuries, to appear in Climatic Change Letters.Google Scholar
  7. Knutson TR, Delworth TL, Dixon KW, Held IM, co-authors (2006) Assessment of twentieth-century regional surface temperature trends using the GFDL CM2 coupled models. J Clim 19:1624–1651CrossRefGoogle Scholar
  8. Maurer EP, Wood AW, Adam JC, Lettenmaier DP, Nijssen B (2002) A long-term hydrologically-based data set of land surface fluxes and States for the conterminous United States. J Clim 15:3237–3251CrossRefGoogle Scholar
  9. Maurer EP, Brekke L, Pruitt T, Duffy PB (2007) Fine-resolution climate change projections enhance regional climate change impact studies. Eos, Trans Am Geophys Union 88(47), 504 (online at
  10. Meehl GA, Tebaldi C (2004) More intense, more frequent, and longer lasting heat waves in the 21st century. Science 305(5686):994–997. doi: 10.1126/science.1098704 CrossRefGoogle Scholar
  11. Meehl, GA, Arblaster JM, Branstator G (2012) Understanding the U.S. East-West differential of heat extremes in terms of record temperatures and the warming hole. J. Clim submittedGoogle Scholar
  12. Nakicenovic N et al (2000) Special report on emissions scenarios: a special report of working group III of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, U.K., 599 ppGoogle Scholar
  13. Pan Z, Arritt RW, Takle ES, Gutowski WJ Jr., Anderson CJ, Segal M (2004) Altered hydrologic feedback in a warming climate introduces a“warming hole”. Geophys Res Lett L17109, doi: 10.1029/2004GL020528
  14. Portmann RW, Solomon S, Hegerl GC (2009) Spatial and seasonal patterns in climate change, temperatures, and precipitation across the United States. Proc Natl Acad Sci USA 106(18):7324–7329Google Scholar
  15. PRISM (PRISM Climate Group, Oregon State University,, created 2007).
  16. Stott PA, Jones GS, Christidis N, Zwiers FW, Hegerl GC, Shiogama H (2010) Single-step attribution of increasing probabilities of very warm regional temperatures to human influence. Atmos Sci Lett 2011, doi: 10.1002/asl.315
  17. Tebaldi C, Arblaster JM, Knutti R (2011) Mapping model agreement on future climate projections. Geophys Res Lett 38:L23701. doi: 10.1029/2011GL049863 CrossRefGoogle Scholar
  18. Wang H, Schubert S, Suarez M, Chen J, Hoerling M, Kumar A, Pegion P (2009) Attribution of the seasonality and regionality in climate trends over the United States during 1950–2000. J Clim 22:2571–2590CrossRefGoogle Scholar
  19. Zwiers FW, Zhang X, Feng J (2011) Anthropogenic influence on extreme daily temperatures at regional scales. J Clim 24(3):881–892CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media B.V. 2012

Authors and Affiliations

  1. 1.Lawrence Livermore National LaboratoryLivermoreUSA
  2. 2.Climate Central, Inc.Palo AltoUSA
  3. 3.National for Atmospheric ResearchBoulderUSA

Personalised recommendations